The present invention relates to a wire cut electric discharge machining apparatus and, more particularly to a device for use in such a wire cut electric discharge machining apparatus for conveying and treating a workpiece, a work or a work scrap cut off from the basic material.
FIG. 1 is a schematic diagram showing a structural view partly in section of an example of a conventional wire cut electric discharge machining apparatus. In this figure, reference numeral 2 designates a wire electrode, and 18 stands for an upper machining solution injection nozzle which is formed of a magnetic material having a dual structure in the diametrical direction thereof. The nozzle 18 includes an electromagnetic coil 19 incorporated into the dual-structure magnetic material coaxially with the wire electrode 2 so as to provide an integral structure. The machining solution injection nozzle 18 (a magnet nozzle) formed of a magnetic material serves as an electromagnet and is thus able to attract and convey a workpiece 10, and a work scrap or a work 9 cut off from the workpiece 10 (see FIG. 3), which is referred simply to as the "work 9" hereinafter when applicable.
More specifically, as shown in FIG. 1, the upper machining solution injection nozzle 18 comprises cylindrically shaped inside yoke 20 having a flange 20a in the upper end thereof and forming an inside ring-shaped magnetic circuit, a cylindrically shaped outside yoke 21 disposed outside of the inside yoke 20 with the upper end thereof in contact with the inner surface of the flange 20a, forming an annular gap between the inside yoke 20 itself and forming an outside ring-shaped magnetic circuit, an electromagnetic coil 19 having a lead wire 19a incorporated integrally into the annular gap between the inside and outside yokes 20 and 21, and a seal member of insulating resin filled in the lower opening in the annular gap to prevent the machining solution entering into the annular gap where the electromagnetic coil 19 is accommodated. Also, the upper machining solution injection nozzle 18 is connected directly to a Z shaft (not shown) and can be moved in a vertical direction.
The inside yoke 20 and outside yoke 21 are made of an iron material having a high magnetic permeability, or a stainless steel material for prevention of rust, or may be made of an iron material on the surface of which anti-rust (rust preventive) plating is then applied. Further, in order to prevent electrolytic corrosion during wire electrical discharge machining, the yokes are wholly or in partly coated with an insulating material. As the insulating coating, either synthetic resin or high wear-proof ceramic coating is generally used.
In FIG. 1, reference numeral 15 designates an upper positioning guide of the wire electrode 2; 16, a lower positioning guide of the wire electrode 2; 17, a stand for carrying the workpiece thereon; and 18a, a lower machining solution injection nozzle.
Now, FIGS. 2 and 3 are explanatory diagrams for the description about the operation of the wire cut electric discharge machining apparatus as shown in FIG. 1.
Next, the operation of the conventional apparatus as shown in FIG. 1 will be described with reference to FIGS. 2 and 3. In FIG. 2, when the wire electrode 2 is removed after the work 9 is machined and detached completely from the workpiece 10, the electromagnetic coil 19 is excited so that a magnetic circuit is constituted by the inside yoke 20, the outside yoke 21 and the work 9. In this case, a magnetic flux is allowed to flow in a direction of an arrow A shown by a broken line in FIG. 2, whereby the work 9 or work scrap can be attracted by the upper machining solution injection nozzle 18 made of a magnetic material.
Then, the work 9, which is attracted by the magnetic force of the upper machining solution injection nozzle 18 as shown in FIG. 3, is taken out in an upward direction (in a direction of an arrow B) from the workpiece 10. Thereafter, the work 9 is conveyed in a horizontal direction (in a direction of an arrow C), and is carried outside of the machining range. The transportation of the work 9 in the upper and horizontal directions is automatically carried out for means by servo controlling the X, Y and Z shafts.
Next, when trying to start afresh the machining of the work 9, after the wire electrode 2 is inserted through the upper and lower machining solution injection nozzles 18 and 18a by use of a wire electrode automatic insertion device (not shown), the upper machining solution injection nozzle 18 is returned to a predetermined height position by means of the Z shaft control, the machining of the work 9 having an arbitrary shape is resumed by means of the X-shaft and Y-shaft control.
Referring now to FIG. 4, there is shown a schematic structural view, partly in section, of another example of the conventional wire cut electric discharge machining apparatus. In FIG. 4, reference numeral 18 also designates an upper machining solution injection nozzle which is made of a magnetic material having a dual structure in the diameter direction thereof. And, the following components are integrally incorporated as one within the dual-structure magnetic material: that is, a ring-shaped permanent magnet 3 disposed concentrically with the wire electrode 2; a ring-shaped movable member 4 made of a magnetic material and movable in a vertical direction; a press spring 5 for biasing the movable member 4 against the permanent magnet 3; an injection port 6 through which an oil, an air or the like for detaching the movable member 4 from the permanent magnet 3 is injected; a case 7 made of a non-magnetic material, and a sealing member 8 formed of a non-magnetic material for filling up a gap in an air pocket (space) 11 formed by the dual-structure magnetic material. The thus constructed upper machining solution injection nozzle 1 is then connected directly to a Z shaft (not shown) in such a manner that it is movable in a vertical direction.
Also, an example of the magnetic material forming the upper machining solution injection nozzle 18 is an iron material having a high magnetic permeability or a stainless steel material for rust prevention, an iron material on the surface of which anti-rust plating may be then applied. Further, in order to prevent electrolytic corrosion during wire electric machining, the upper machining solution injection nozzle 18 is whole or partly coated with an insulating material. As the insulating coating, generally, a synthetic resin coating or a highly wear proof ceramic coating is used.
In FIG. 4, the other portions or members which are common to those in FIGS. 1 to 3 bear the same or corresponding reference numerals in FIGS. 1 to 3.
The operation of the conventional wire cut electric discharge machining apparatus as shown in FIG. 4 will be described hereinafter. In FIG. 4, as is similar to the operation of the above described conventional apparatus, when the wire electrode 2 is removed after the work 9 has been machined and is then detached completely from the workpiece 10, the air present in the air pocket 11 within the magnetic material forming the machining solution injection nozzle 1 is discharged. Thereafter, if the machining solution injection nozzle 18 is caused to approach the work 9 with the movable member 4 in contact with the permanent magnet 3, a magnetic flux flows in a direction of an arrow A shown in FIG. 9 through a magnetic circuit formed by the machining solution injection nozzle 18, permanent magnet 3 and work 9, so that the work 9 can be attracted by the magnetic force of the machining solution injection nozzle 18. The work 9 attracted by the magnetic force of the machining solution injection nozzle 18 in this manner, after taken out in an upward direction, that is, in a direction of arrow B shown in FIG. 4, is conveyed in a horizontal direction, that is, in a direction of arrow C shown in FIG. 4. Then, the work 9 is carried outside of the machining range. The transportation of the work 9 in the upward direction (B direction) and in the horizontal direction (C direction) is automatically carried out by means of servo controlling the X, Y and Z shafts.
After the work 9 is carried to a predetermined position outside of the machining range, the air is injected through the injection port 6 into the air pocket 11 to detach the movable member 4 from the permanent magnet 3 to thereby expand the magnetic gap within the magnetic circuit and thus reduce the magnetic flux which passes through the work 9 being attracted. That is, the work 9 can be dropped from the machining solution injection nozzle 19 at the time when the weight of the work 9 exceeds the magnetic force for attracting the work 9. The following machining operation will be carried out in the same manner as described in the above described conventional apparatus.
With such a conventional wire cut electric discharge machining apparatus shown in FIG. 1, as the upper machining solution injection nozzle 18 is attracting the work 9 to lift the same, the amount of heat generated due to the current flowing through the electromagnetic coil 19 is increased thereby resulting in deteriorating the machining accuracy of the work 9. This has been a problem to be solved in the conventional wire cut electric discharge machining apparatus. Also, when a power failure occurs while the work or work scrap is being attracted to be removed form the workpiece 10, then the magnetic force of the magnetic material forming the machining solution injection nozzle 18 is extinguished abruptly to thereby cause the work or work scrap to fall down resulting in an occurrence of damage in the work 9, which may be the surface of a table (not shown) or the like. Further, there may occur the same damage to the work 9 and the like due to the fact that the work 9 or the work scrap is incompletely attracted or held by the nozzle 18.
In view of this problem, in order to prevent such drop of the work or work scrap, it has been proposed to employ an optical sensor capable of detecting the attraction condition externally during the operation of attracting the work or work scrap. In this case, however, it is disadvantageous in that it is difficult to detect the attraction of small-size work scraps and since the position where the detection should be carried out is changeable, it is troublesome to fix or limit the detection position.
Further, in the conventional apparatus, it is difficult to detect the attraction condition with accuracy, to detect the drop of the work 9 and the like from the nozzle 18 during conveying thereof, and to detect the delivery of the work 9 and the like into a work collecting box (not shown). This may result in making it impossible to continue further machining operation.
With another conventional wire electric discharge machining apparatus as shown in FIG. 4, a movable mechanism which includes a movable member capable of being moved by oil, air or the like must be held within the magnetic material forming the machining solution injection nozzle, resulting in the complicated structure. In such structure, there are possibilities that undesired substances such as sludges contained in the oil, air or the like, water and the like may be mixed and thus a periodic maintenance is necessary to remove such undesired substances. Also, due to the provision of the movable mechanism including the movable member, it is very difficult to reduce the size of the machining solution injection nozzle.